The micronucleus (MN) assay is the most widely utilized in vivo genotoxicity assay and is recommended for the safeLy evaluation of new chemicals and formulations by regulatory agencies worldwide. The aim of this research program is to evaluate whether modifications to our validated flow cytometry (FCM) based mouse MN assay can be used to accurately measure MN frequencies in the hone marrow and peripheral blood of rats. The rat bone marrow assay is currently performed using traditional microscopic methods, which are costly, tedious and time- consuming. Since rats are the most widely used rodent in toxicology and pharmacokinetic studies, a rat peripheral blood test system would be extremely useful for integrating in vivo endpoints and for significantly decreasing animal requirements. If a sensitive micronucleus test could be integrated into other rat studies, preliminary information regarding potential genotoxicity would be obtained without the use of additional animals or additional test material. An automated method of detecting clastogenic activity in rats would represent a significant advance over existing methods in terms of turnaround-time, cost and reliability. Experiments are planned to:l) determine methods for the accurate analysis of rat peripheral blood and bone marrow MN by FCM; and 2) evaluate the latitude of subchronic dosing and bleeding regimens when measuring peripheral blood MN and the ability to integrate the MN endpoint with these studies. By utilizing FCM in conjunction with proper fixing and staining procedures we hope to develop a reliable method to enumerate MN in rat peripheral blood and hone marrow. Automation of these measurements would enable Litron to offer another technologically innovative and improved genetic toxicology service. These test systems will offer significant advantages over existing protocols by increasing the sensitivity and efficiency, while simultaneously decreasing the number of animals used in genetic toxicology testing. This method offers enormous commercial potential as industry would save money, animals, test material and time contracting out MN analyses to an expert facility such as Litron. PROPOSED COMMERCIAL APPLICATIONS: An automated method of detecting micronuclei in the peripheral blood and bone marrow of rats would represent a significant advance over existing methods in terms of turn-around-time, cost and reliability. The proposed research initiative will further establish Litron Laboratories as an expert testing facility which provides industry, academia and government with highly reliable genotoxicity data. We plan to develop a research kit which would include reagents necessary for researchers to obtain blood samples for subsequent MN analyses by Litron.